This invention relates to an improved excavation apparatus, and in particular to an improved underwater excavation apparatus.
Underwater excavation apparatus are known, eg, from GB 2 240 568 (CONSORTIUM RESOURCE et al). In that disclosure there is described. an underwater excavation apparatus comprising a hollow body with an inlet to receive water and an outlet for discharge of water. A propeller is rotatably mounted in the hollow body to draw water through the inlet and deliver a flow 6f water through the outlet. Water jets on the propeller tips rotate the propeller when water is supplied to the jets.
Such rotation causes water to be drawn into the body through the inlet and expelled from the body as a flow through the outlet. The flow can be used to displace material on the seabed.
Known prior art underwater excavation apparatus suffer from a number of problems/disadvantages, for example:
(a) Low energy efficiency due to e.g. hydrodynamic limitations of fluid jets, thus requiring extremely large and power hungry pumps to drive the system);
(b) tendency of apparatus to rotate in reaction to rotation of the propeller;
(c) difficulty in steering and positioning of the apparatus.
It is an object of at least some of the aspects of the present invention to seek to obviate or mitigate one or more of the aforementioned problems in the prior art.
According to a first aspect of the present invention there is provided an underwater excavation apparatus comprising a hollow body having at least one inlet and at least one outlet, at least one pair of impellers rotatably mounted in the hollow body and means for driving the impellers.
Advantageously, the driving means cause the impellers to be driven in contrary rotating directions, in use.
The at least one inlet may be inclined at an angle to an axis along which the at least one outlet is provided.
Preferably, there is provided at least one pair of inlets.
Preferably, the at least one pair of inlets are substantially symmetrically disposed around an axis extending from the outlet.
In one embodiment the underwater excavation apparatus comprises a pair of horizontally opposed inlets communicating with a single outlet, the outlet being disposed vertically downwards substantially midway between the two inlets, in use. In this case, the excavation apparatus is, therefore, substantially xe2x80x9cTxe2x80x9d shaped in profile.
In an alternative embodiment the underwater excavation apparatus comprises a pair of inlets communicating with a single outlet, the inlets being substantially symmetrically disposed around an axis extending from the outlet, the outlet being disposed vertically downwards substantially midway between the two inlets, in use. In this case, the excavation apparatus is, therefore, substantially xe2x80x9cYxe2x80x9d shaped in profile.
Advantageously, the outlets are each spaced/inclined substantially 45xc2x0 from the axis extending from the outlet.
At least one impeller may be provided within/adjacent each inlet.
The means for driving the/each impeller(s) may include at least one drilling motor.
The at least one drilling motor may comprise a stator and a rotor rotatably mounted in the stator, the stator being provided with a rod recess and an exhaust port, the rotor being provided with a rotor channel and at least one channel for conducting motive fluid from the rotor channel to a chamber between the rotor and the stator, the rod recess being provided with a rod which, in use, forms a seal between the stator and the rotor.
Although not essential it is highly desirable that the rotor be provided with a seal for engagement with the stator.
Preferably, the seal is made from a material selected from the group consisting of plastics materials, polyethylethylketone, metal, copper alloys and stainless steel.
Advantageously, the rod is made from a material selected from the group consisting of plastics materials, polyethylethylketone, metal, copper alloys and stainless steel.
Preferably, the stator is provided with two rod recesses which are disposed opposite one another, and two exhaust ports which are disposed opposite one another, each of the rod recesses being provided with a respective rod, the rotor having two seals which are disposed opposite one another.
The drilling motor may advantageously comprise two drilling motors arranged with their respective rotors connected together each motor comprising a stator and a rotor rotatably mounted in the stator, the stator being provided with a rod recess and an exhaust port, the rotor being provided with a rotor channel and at least one channel for conducting motive fluid from the rotor channel to a chamber between the rotor and the stator, the rod recess being provided with a rod which, in use, forms a seal between the stator and the rotor.
Preferably, the drilling motors are connected in parallel, although they could be connected in series if desired.
Advantageously, the drilling motors are arranged so that, in use, one drilling motor operates out of phase with the other. Thus, in a preferred embodiment each drilling motor has two chambers and the chambers in the first drilling motor are 90xc2x0 out of phase with the chambers in the second drilling motor. Similarly, in an embodiment in which each drilling motor has four chambers, the chambers in the first drilling motor would preferably be 45xc2x0 out of phase with the chambers on the second drilling motor. This arrangement helps ensure a smooth power output and inhibits stalling.
Alternatively, the at least one drilling motor may be a xe2x80x9cMoineauxe2x80x9d, hydraulic or a suitably adapted electric motor.
The impellers may be driven by means of a gearbox or by exploitation of the opposing reactive torque on a drive body of the motor.
When the reactive torque upon the motor body is utilised, at least one impeller may be connected to an output shaft of said motor, while at least one other impeller may be connected to the motor body.
Alternatively the impellers may be driven by a pair of motors operating in opposite directions. In such case said motors and impellers are balanced and equal.
The underwater excavation apparatus may further comprise an agitator device having mechanical disturbance means and fluid flow disturbance means.
The underwater excavation apparatus may, in use, be suspended from a surface vessel or mounted upon a sled of the type currently known for use in subsea excavation operations.
According to a second aspect of the present invention there is provided an underwater apparatus comprising a hollow body having a pair of inlets communicating with an outlet, at least one pair of impellers rotatably mounted in the hollow body and means for driving the impellers, the inlets being substantially symmetrically disposed around an axis extending from the outlet, wherein the inlets are not horizontally opposed to one another.